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dchandler 2003-07-14 12:22:29 +00:00
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/*
* ====================================================================
*
* The Apache Software License, Version 1.1
*
* Copyright (c) 1999-2003 The Apache Software Foundation. All rights
* reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
*
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
*
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in
* the documentation and/or other materials provided with the
* distribution.
*
* 3. The end-user documentation included with the redistribution, if
* any, must include the following acknowlegement:
* "This product includes software developed by the
* Apache Software Foundation (http://www.apache.org/)."
* Alternately, this acknowlegement may appear in the software itself,
* if and wherever such third-party acknowlegements normally appear.
*
* 4. The names "The Jakarta Project", "Commons", and "Apache Software
* Foundation" must not be used to endorse or promote products derived
* from this software without prior written permission. For written
* permission, please contact apache@apache.org.
*
* 5. Products derived from this software may not be called "Apache"
* nor may "Apache" appear in their names without prior written
* permission of the Apache Group.
*
* THIS SOFTWARE IS PROVIDED ``AS IS'' AND ANY EXPRESSED OR IMPLIED
* WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
* DISCLAIMED. IN NO EVENT SHALL THE APACHE SOFTWARE FOUNDATION OR
* ITS CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
* SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
* LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF
* USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND
* ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY,
* OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT
* OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
* SUCH DAMAGE.
* ====================================================================
*
* This software consists of voluntary contributions made by many
* individuals on behalf of the Apache Software Foundation. For more
* information on the Apache Software Foundation, please see
* <http://www.apache.org/>.
*
*/
package org.apache.commons.jrcs.diff.myers;
import org.apache.commons.jrcs.diff.*;
/**
* A clean-room implementation of
* <a href="http://www.cs.arizona.edu/people/gene/">
* Eugene Myers</a> differencing algorithm.
* <p>
* See the paper at
* <a href="http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps">
* http://www.cs.arizona.edu/people/gene/PAPERS/diff.ps</a>
*
* @version $Revision: 1.1 $ $Date: 2003/07/14 12:22:30 $
* @author <a href="mailto:juanco@suigeneris.org">Juanco Anez</a>
* @see Delta
* @see Revision
* @see Diff
*/
public class MyersDiff
implements DiffAlgorithm
{
/**
* Constructs an instance of the Myers differencing algorithm.
*/
public MyersDiff()
{
}
/**
* {@inheritDoc}
*/
public Revision diff(Object[] orig, Object[] rev)
throws DifferentiationFailedException
{
PathNode path = buildPath(orig, rev);
return buildRevision(path, orig, rev);
}
/**
* Computes the minimum diffpath that expresses de differences
* between the original and revised sequences, according
* to Gene Myers differencing algorithm.
*
* @param orig The original sequence.
* @param rev The revised sequence.
* @return A minimum {@link PathNode Path} accross the differences graph.
* @throws DifferentiationFailedException if a diff path could not be found.
*/
public static PathNode buildPath(Object[] orig, Object[] rev)
throws DifferentiationFailedException
{
if (orig == null)
throw new IllegalArgumentException("original sequence is null");
if (rev == null)
throw new IllegalArgumentException("revised sequence is null");
// these are local constants
final int N = orig.length;
final int M = rev.length;
final int MAX = N + M + 1;
final int size = 1 + 2 * MAX;
final int middle = (size + 1) / 2;
final PathNode diagonal[] = new PathNode[size];
PathNode path = null;
diagonal[middle + 1] = new Snake(0, -1, null);
for (int d = 0; d < MAX; d++)
{
for (int k = -d; k <= d; k += 2)
{
final int kmiddle = middle + k;
final int kplus = kmiddle + 1;
final int kminus = kmiddle - 1;
PathNode prev = null;
int i;
if ( (k == -d) ||
(k != d && diagonal[kminus].i < diagonal[kplus].i))
{
i = diagonal[kplus].i;
prev = diagonal[kplus];
}
else
{
i = diagonal[kminus].i + 1;
prev = diagonal[kminus];
}
diagonal[kminus] = null; // no longer used
int j = i - k;
PathNode node = new DiffNode(i, j, prev);
// orig and rev are zero-based
// but the algorithm is one-based
// that's why there's no +1 when indexing the sequences
while (i < N && j < M && orig[i].equals(rev[j]))
{
i++;
j++;
}
if (i > node.i)
node = new Snake(i, j, node);
diagonal[kmiddle] = node;
if (i >= N && j >= M)
{
return diagonal[kmiddle];
}
}
diagonal[middle+d-1] = null;
}
// According to Myers, this cannot happen
throw new DifferentiationFailedException("could not find a diff path");
}
/**
* Constructs a {@link Revision} from a difference path.
*
* @param path The path.
* @param orig The original sequence.
* @param rev The revised sequence.
* @return A {@link Revision} script corresponding to the path.
* @throws DifferentiationFailedException if a {@link Revision} could
* not be built from the given path.
*/
public static Revision buildRevision(PathNode path, Object[] orig, Object[] rev)
{
if (path == null)
throw new IllegalArgumentException("path is null");
if (orig == null)
throw new IllegalArgumentException("original sequence is null");
if (rev == null)
throw new IllegalArgumentException("revised sequence is null");
Revision revision = new Revision();
if (path.isSnake())
path = path.prev;
while (path != null && path.prev != null && path.prev.j >= 0)
{
if(path.isSnake())
throw new IllegalStateException("bad diffpath: found snake when looking for diff");
int i = path.i;
int j = path.j;
path = path.prev;
int ianchor = path.i;
int janchor = path.j;
Delta delta = Delta.newDelta(new Chunk(orig, ianchor, i - ianchor),
new Chunk(rev, janchor, j - janchor));
revision.insertDelta(delta);
if (path.isSnake())
path = path.prev;
}
return revision;
}
}